DNA Fingerprinting Osama Bin Laden

This morning I saw several tweets about DNA testing and Osama Bin Laden:

“All I’m sayin is,if they took DNA samples for bin Laden,who did they match it against,& that was one ruddy fast PCR,can I have your machine?” – upulie

“Did they bring PCR machine on the site to confirm Bin Laden’s death?” – seanjeon

The US military used DNA to identify Osama Bin Laden very quickly after he was killed. How? Although we don’t have intimate knowledge of Osama’s DNA identification, here’s one way that OpenPCR could potentially be used in a similar situation.

What’s DNA Fingerprinting?

DNA fingerprinting compares a sample of DNA to a previously verified sample. In Osama Bin Laden’s case, there were samples of his relative’s DNA available so a rough DNA fingerprint was on hand. The job of the scientists was to quickly analyze the new DNA sample and see if it matched what was on file.

Fingerprinting begins with a DNA sample. A quick and easy source of DNA is spit. Spit has cheek cells in it and every cheek cell has a copy of the entire human genome. The human genome is 3 billion pieces of information. As comparison, a Tweet contains up to 140 letters, so 21 million tweets to send out your genome (or Osama’s genome for that matter)! Even with recent leaps in biotechnology, reading all that DNA today costs a lot of money (thousands of dollars) and time (about a month).

We’re all a little bit different…

Luckily there’s a shortcut for quick DNA identification instead of sequencing the entire genome. Some bits of DNA are very important (like one letter that determines your ability to taste bitterness), while others vary a lot between people without a clear function. It’s these highly variable sections that are used for DNA fingerprinting because they differ greatly between individuals, but are similar between relatives. In the case of Osama Bin Laden, however a reference sample of his DNA was not available. Instead, samples from family members were used to compile his fingerprint.

The internationally accepted standard for DNA fingerprinting uses 13 STRs (short tandem repeats) to create a unique fingerprint. A short tandem repeat is 1 to 4 letters of DNA that is found repeating over and over in the human genome. For instance, one gene used for DNA fingerprinting contains a repeated pattern of “CTTT”, i.e. “CTTTCTTTCTTTCTTT”. This is from the FGA gene in humans, and it has been seen repeating from 12 to 50 times. By looking at the number of repeats in all 13 STRs, a unique fingerprint is created for each person.

Do it yourself

The tools for doing this type of analysis are accessible to hobbyists with a budget.

First, extract the DNA from your spit sample.

You can practice with stuff in your kitchen after watching this video on extracting DNA from a banana:

Next, you’ll need a PCR machine such as OpenPCR, which is like a xerox machine for DNA. Starting with a small DNA sample such as a spit sample, a PCR machine will selectively copy just the 13 STR sequences. You’ll also need short pieces of DNA primers to copy each STR. The DNA sequences for all 13 STR primers are available here.

Finally, use gel electrophoresis to visualize the DNA after PCR. Gel electrophoresis is a tool for measuring DNA. With the earlier example of FGA for instance, gel electrophoresis can tell you how many copies of the “CTTT” pattern are in the sample genome. By looking at the length of all the STR primers you’ll have a fingerprint unique to yourself.

If you’re fingerprinting a friend, you will need to take extra precautions to make sure your own DNA does not contaminate the experiment. For instance, just coughing on the DNA sample could ruin your experiment, since you’ll end up fingerprinting yourself. DNA fingerprinting is a bit more complicated than can be explained in this quick article, but post in the comments if you’re interested. And that’s how DNA fingerprinting works!